United States Patent m [ii] 4,158,617 Winter [45] Jun. 19, 1979

[54] METHOD FOR THE PRODUCTION OF 3,380,935 4/1968 Ring 252/512 SUPERCONDUCTORS CONSISTING OF A 3,427,264 2/1969 Forster et al 260/42.22 POLYMER OF GLASS MATRIX WITH 3,450,510 6/1969 Calows 264/108 FINELY DISPERSED PARTICLES 3,626,041 12/1971 Fields et al 264/108 3,650,991 3/1972 Watson 252/512 [75] Inventor: Heinrich Winter, Eschborn, Fed. 3,760,495 9/1973 Meger 264/104 Rep. of Germany 3,846,345 11/1974- Mason et al 252/512 3,867,315 2/1975 Tigner et al 252/512 [73] Assignee: Battelle-Institute e.V., Frankfurt am 3,988,524 10/1976' Dreyer et al 260/42.22 Main, Fed. Rep. of Germany 4,013,591 3/1977 Granger et al 252/518 [21] Appl. No.: 787,438 FOREIGN PATENT DOCUMENTS [22] Filed: Apr. 14, 1977 2363279 7/1974 Fed. Rep. of Germany 260/42.22

[30] Foreign Application Priority Data Primary Examiner—Ja.y H. Woo Apr. 14, 1976 [DE] Fed. Rep. of Germany 2616394 Attorney, Agent, or Firm—Fisher, Christen & Sabol [51] Int. C1.2 B29D3/02 [57] ABSTRACT [52] U.S. CI 264/108; 264/176 R; A method is disclosed for the production of supercon- 264/211; 252/512; 252/518; 427/62; 427/205 ductors consisting of a polymer or glass matrix which [58] Field of Search 264/108, 104, 24, 176 R, 264/176 F; 260/42.22; 106/193 M; 252/500, contains a very fine dispersion of superconducting par- 512, 5; 427/62, 205; 343/911 R ticles, approximately 50 to 100 A in diameter, of inter- metallic compounds of vanadium or niobium with the [56] References Cited elements aluminum, germanium, silicon, gallium or tin, U.S. PATENT DOCUMENTS or of niobium nitride or niobium carbonitride. The ma- trix material is first brought into a viscous state and the 2,593,943 4/1952 Wainer 260/42.22 superconducting particles are admixed with the viscous 2,721,357 10/1955 Hochberg 264/104 2,761,849 9/1956 Coler 106/193 M matrix in such quantities that, after solidification of the 2,847,710 8/1958 Pitzer 264/63 matrix, the particles are spaced at an average distance of 3,015,858 1/1962 Hendricks 264/108 10 to 100 A. The superconducting material may be then 3,148,232 9/1964 Scheyer 264/108 formed in wires, filaments and tapes. 3,167,525 1/1965 Thomas : 260/42.22 3,300,329 1/1967 Orsino et al 260/42.22 3,328,501 6/1967 Barnett 264/108 18 Claims, No Drawings 4,152. 386 2 /3W/A15 structure, instead of low-melting supercon- METHOD FOR THE PRODUCTION OF ducting metals and alloys, such as lead, lead-40 weight SUPERCONDUCTORS CONSISTING OF A percent bismuth, tin, mercury and indium, and thus to POLYMER OF GLASS MATRIX WITH FINELY arrive at transition temperatures in the range of the DISPERSED PARTICLES 5 temperature of liquid hydrogen and at critical magnetic fields extending into the megagauss range. Moreover, FIELD OF THE INVENTION the technology described in detail by J. H. P. Watson in The invention relates to a method for the production his U.S. Pat. No. 3,748,728 of July 31, 1973, For exam- of superconductors consisting of a polymer or glass ple, particles of low-melting superconductors of the matrix which contains a very fine dispersion of super- 10 first kind can be dispersed only in zones close to the conducting particles, about 50 to 1000 A in diameter, of surface of the glass. The greater part of the glass cross intermetallic compounds of vanadium or niobium with section thus cannot be utilised for superconduction. Nor the elements aluminium, germanium, silicon, gallium or was it possible to prepare ductile thin filaments or tapes tin, or of niobium nitride or niobium carbonitride. as required for superconducting magnetic coils. BRIEF DESCRIPTION OF THE PRIOR ART 15 Furthermore, attempts have been reported to prepare particles with a size in the /xm-range from "hard" and Heavy-duty "hard" superconductors of the conven- extremely brittle superconducting materials by grinding tional type with a transition temperature of 15 K or in a ball mill (H. R. Khan and Ch. J. Raub, J. Less-Com- above are without exception extremely brittle sub- mon Metals 43 (1975) pp. 49-54). However, in order to stances and thus cannot be transformed into extended 20 achieve superconductivity by the above-described ef- conductors, e.g. wires. Therefore, attempts have been fect, particles with diameters between 50 and 1000 A reported to incorporate these "hard" superconductors are required. For their preparation E. Neueschwander of "the second kind" in the form of small particles into (E. Neuenschwander. J. Less-Common Metals 11 a metallic matrix, e.g. a copper matrix. As a result of the (1966) pp. 365-375) has proposed a method in which proximity effect, the particles incorporated in the ma- 25 chlorides of niobium together with nitrogen and/or trix influence their electrically conductive, though non- hydrocarbon are injected into a hydrogen plasma where superconducting, metallic environment such that super- the following reaction takes place: conduction-inducing electron pairs with opposite spin, 2NbCl + N +5H2—• 2NbN +10HC1. called Cooper pairs, are generated also there, so that 5 2 ultimately the entire composite system of metal and 30 As a result of this reaction, niobium nitride particles superconducting particles becomes a superconductor. of the required size are precipitated from the reaction A prerequisite for this is that the distances between the zone which has a temperature of about 3000° C. Nio- incorporated superconducting particles do not exceed bium nitride is a "hard" superconductor with a transi- the "coherence length" which may be of the order of tion temperature of about 15 K (N. Pesall et al., Appl. 103 A. 35 Phys. Lett. 7 (1965) pp. 38-39). In the same way nio- An entirely new method of incorporating supercon- bium carbonitride particles can be prepared by the addi- ducting particles into a non-superconducting and elec- tion of a hydrocarbon, e.g. C2H2. NbCxNi-^, with trically non-conductive matrix was found by J. H. P. values of x up to 0,5, shows transition temperatures Watson (Appl. Phys. Lett. 15 (1969) pp. 125-127. He above 17 K (N. Pesall et al., see above). leached pores with a diameter of about 20 to 30 A into 40 If, instead of nitrogen and hydrocarbon, chlorides of the surfaces of Vycor glasses and filled these under aluminium, germanium, gallium, silicon or tin, in partic- hydrostatic pressure with liquid lead. In this way he ular, are introduced into the reaction zone together obtained lead particles in a glass matrix which had the with chlorides of niobium or vanadium, high-melting above diameter and were spaced at a distance only "hard" superconductors of the type A3B (A denoting somewhat less than that. Although these particles were 45 Nb or V, B for Al, Ge, Ga Si or Sn) with the desired separated from each other by the dielectric glass, they /JW/A15-structure are obtained upon proper dosage. showed significantly enhanced superconducting prop- erties. The critical magnetic field for lead was raised by SUMMARY OF THE INVENTION a factor of 200. The soft superconductor of the first The objective of this invention is to exploit the find- kind, i.e. the metal lead, turned into a "hard" supercon- 50 ings outlined above and to incorporate particles of high- ductor of the second kind. melting "hard" superconductors of the second kind into In the above-cited article J. H. P. Watson further an electrically non-conductive polymer of glass matrix points out that the transition temperature Tc as well can for the purpose of preparing a superconductive material be raised significantly if superconducting particles with of the above-defined type. This is possible if, as pro- a size and a spacing of the order of 10 A are successfully 55 posed by this invention, the matrix material is brought incorporated into an electrically non-conductive ma- into a viscous stage and the superconducting particles trix. According to McMillan's theory (Phys. Rev. 167 with diameters between 50 and 1000 A are admixed to (1968) p. 331) this will increase the transition tempera- this liquid or solution in such quantities that after solidi- ture from about 10 to 20 K for niobium and from about fication of the matrix material the finely dispersed parti- 17 to 40 K for V3Si. The increase is ascribed to the 60 cles are spaced at an average distance of the order of 10 tunnel effect. The electrons combined into Cooper pairs to 100 A. can tunnel through the distances between the dispersed Because of their high melting point and their stability superconducting particles; it is said to be of advantage if the superconducting particles remain unchanged in the the matrix separating the particles is a non-conductor. molten glass or the dissolved polymer. J. H. P. Watson failed in all his involves a number of 65 The method according to the invention eliminates the serious disadvantages, to incorporate into the glass necessity of leaching the glass surface and filling the pores "hard" superconductors, such as niobium and resulting pores with molten metal under hydrostatic intermetallic compounds of niobium or vanadium of pressure. In addition, the whole cross section of the 4,152,386

5 2 polymer or glass can now be utilised for superconduc- critical current density Ic~ 10 A/cm , upper critical ting purposes. The further processing of polymers is magnetic field strength 370 kG. quite easy because of their good plastic and thermoplas- To this end low-melting glasses are ground into pow- tic properties. Glasses can readily be spun into filaments der and fractionated by sedimentation, A fraction with and tapes after introduction and distribution of the su- a particle size below 3 fim is selected and intimately perconducting particles. During the spinning process mixed with NbN particles with an average size of 90 A the incorporated superconducting particles are ar- in a ratio of about 70 to 30 volume percent. The mixture ranged in rows along the flow lines at very narrow is subsequently filled into a ball mill together with a spacings in the direction of the filament; this improves low-boiling liquid, e.g. a hydrocarbon such as benzene, the superconducting properties additionally. 10 and a small quantity of a wetting agent, e.g. a fatty acid Additional features, advantages and applications of or paraffin. Prior to this the ball mill was heated to a the invention are described in the following and illus- temperature near the boiling point of the low-boiling trated by specific examples. liquid. After a short mixing period the entire mixture becomes pasty. In this state the mixture is pressed into DETAILED DESCRIPTION OF THE 15 PREFERRED EMBODIMENTS rods which are dried at a temperature below 700° C. The resulting sintered rods have only unsatisfactory A superconductor with technically advanced proper- superconducting properties. After drawing filaments ties can be produced by admixing 30 volume percent from these rods at a temperature below 850° C. — this NbN particles with mean diameter of 90 A to 70 volume is a conventional method — opaque filaments with a percent low-density polyethylene at temperatures of up 20 diameter between 50 and 120 fxm were obtained. As to about 170° C. and distributing the particles uniformly expected, these had the superconducting properties by extended kneading or stirring. Adding wetting described above. agents such as paraffin or fatty acids to the polymer or applying these agents to the particles enhances uniform It is also of advantage to deposit the superconducting distribution in the matrix. The resulting material can be 25 particles on to or incorporate them into polymers which extruded to strip. The strip has a transition temperature do not completely embrittle even at low temperatures, of 17 K, a critical magnetic field strength of about 350 e.g. ethylene-vinyl acetate or ethylene-ethyl acrylate. kG, and a critical current density of 7 X104 A/cm2. If a The softening point of these polymers ranges between higher thermal conductivity is required the strip can be 65° and 95° C. They can be filled with a particularly high proportion of superconducting particles. Addi- coated with a metal, e.g. copper, on both sides. 30 Using superconducting V3Si particles makes it the to tional materials suitable for particle incorporation, are achieve transition temperatures of up to 27 K in this butadiene-based polymers. way. I claim: Particularly uniform distribution of the superconduc- 1. A method for the production of superconductors ting particles in the polymer matrix can be achieved by 35 consisting of a polymer or glass matrix with incorpo- introducing them into a polymer-solvent solution where rated finely dispersed superconducting particles, about upon the solvent is evaporated. A lacquer of this kind 50 to 1000 A in diameter, of intermetallic compounds of containing about 65 volume percent superconducting vanadium or niobium with the elements of aluminium, particles can be used for coating metallic and nonmetal- germanium, silicon, gallium or tin or of niobium nitride lic carriers with a superconductor. In this case it is of 40 or niobium carbonitride, comprising the steps of: (a) special advantage to deposit alternately a coat of lac- converting the matrix material into a viscous state; and quer with superconducting particles and a coat of lac- (b) admixing superconducting particles to this viscous quer with finely dispersed metal particles, e.g. silver matrix in such quantities that after solidification of the powder. The resultant composite lacquer exhibits a matrix material the incorporated particles are spaced at significantly improved thermal conductivity. A disper- 45 a mean distance of the order of 10 to 100 A. sion of superconducting plus metal particles in the lac- 2. A method according to claim 1, wherein the matrix quer can also be used to advantage. material is a polymer and the particles are suspended in In the following it is described how a superconductor a solvent for admixture to the viscous polymer. is prepared by providing a thin polyester strip with a 3. A method according to claim 2, comprising the lacquer coating of this kind. After the NbN particles 50 further steps of depositing the viscous polymer with the have been added to the lacquer solution the latter is incorporated particles on a carrier, and causing it to mixed in a ball mill together with phenolic and silicone solidify. resins for several hours. The filtered solution is then 4. A method according to claim 3, comprising the squeezed through slot dies and applied to the carrier as further step of admixing additional metal particles to the a thin film (12 |im). While the lacquer is dried in a dry- 55 viscous polymer with the incorporated particles. ing tunnel in a dustfree atmosphere the solvent con- 5. A method according to claim 1 comprising the tained in the lacquer evaporates and the superconduc- additional step of adding a wetting agent to enhance the ting layer is cured. The final layer is about 6 jxm thick. uniform distribution of the particles in the matrix. At a volume content of NbN particles of about 55 per- 6. A method according to claim 1 wherein the matrix cent (mean particle size 90 A) incorporated in the lac- 60 material is a plastic on the basis of an olefin polymer or quer coating the transition temperature achieved is 19 a butadiene polymer. K, the critical current density related to the lacquer 5 2 7. A method according to claim 6 wherein the plastic coating at 4.2 K 2X10 A/cm and the upper critical is selected from the group consisting of polyethylene, magnetic field strength HC2 about 700 kG. ethylene-vinyl acetate, ethylene-ethyl acrylate, or a Incorporating the same kind of NbN particles in a 65 polyene such as trans-polyacetylene. glass melt (30 vol. %) enables the following characteris- 8. A method according to claim 3, comprising the tics to be achieved after processing into fibers with a step of depositing suspension of the superconducting diameter of about 120 /j,m: transition temperature 18 K, particles on a carrier in the form of a lacquer. >2,386 6 9. A method according to claim 8, comprising the ing filaments, films or strip from this mass and subse- steps of alternating lacquer coatings with superconduc- quently solidified by cooling or drying processes. ting particles with lacquer coatings with metallic parti- 14. A method according to claim 13, wherein the cles. matrix material in powder form is intimately mixed with 10. A method according to claim 8, wherein the lac- 5 the superconducting particles, pressed and/or sintered quer coating contains suspended metallic particles in before being processed into filaments, films or strip. addition to the superconducting particles. 15. A method according to claim 13 wherein the 11. A method according to claim 8, wherein the lac- matrix is converted irito a viscous state by heating. quer coatings are continuously deposited on to a carrier 16. A method according to claim 13 wherein the film, e.g. a polyester film. 10 matrix is converted into a viscous state by contacting 12. A method according to claim 5 wherein a fatty with a solvent. acid or paraffin is used as wetting agent. 17. A method according to claim 13 wherein the 13. A method for producing filaments, film or strip filaments, film or Strips are formed by spinning. from a superconducting material comprising the steps 18. A method according to claim 13 wherein the of converting the matrix material with incorporated 15 filaments, films or strips are formed by drawing. superconducting particles into a viscous state, and form- *****

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